CVE-2013-4399 in libvirt
Summary
by MITRE
The remoteClientFreeFunc function in daemon/remote.c in libvirt before 1.1.3, when ACLs are used, does not set an identity, which causes event handler removal to be denied and remote attackers to cause a denial of service (use-after-free and crash) by registering an event handler and then closing the connection.
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Analysis
by VulDB Data Team • 04/22/2023
The vulnerability described in CVE-2013-4399 represents a critical security flaw within the libvirt virtualization management library that affects versions prior to 1.1.3. This issue specifically manifests in the remoteClientFreeFunc function located in daemon/remote.c, where the absence of proper identity setting during connection termination creates a dangerous condition that can be exploited by remote attackers to execute denial of service attacks. The flaw occurs exclusively when Access Control Lists (ACLs) are enabled within the libvirt environment, making it particularly concerning for systems that rely on proper authentication and authorization mechanisms.
The technical root cause of this vulnerability stems from improper memory management and identity handling within the libvirt daemon's event processing subsystem. When a client connection is closed while an event handler is registered, the remoteClientFreeFunc function fails to establish the appropriate identity context before proceeding with cleanup operations. This omission creates a use-after-free condition where the event handler removal process attempts to access memory that has already been freed, leading to unpredictable behavior and potential system crashes. The vulnerability is classified under CWE-415 as an improper handling of memory allocation and deallocation, specifically involving double-free conditions and use-after-free scenarios that are particularly dangerous in daemon processes.
The operational impact of this vulnerability extends beyond simple service disruption, as it can be exploited by remote attackers to cause complete system instability within virtualization environments. An attacker who successfully exploits this vulnerability can register an event handler, establish a connection to the libvirt daemon, and then close the connection in a manner that triggers the use-after-free condition. This attack vector is particularly dangerous because it can be executed without requiring elevated privileges or specific authentication credentials, making it accessible to any remote user who can establish a connection to the vulnerable service. The resulting crash can lead to complete daemon termination, effectively denying all virtualization services to legitimate users and potentially causing data loss or service interruption across virtualized environments.
From a cybersecurity perspective, this vulnerability aligns with several ATT&CK techniques including T1499.004 for Network Denial of Service and T1068 for Exploitation for Privilege Escalation, though in this case the attack specifically targets service availability rather than privilege escalation. The vulnerability demonstrates the importance of proper memory management in daemon processes and highlights the risks associated with incomplete identity handling in multi-threaded environments. Organizations using libvirt for virtualization management should prioritize immediate patching to version 1.1.3 or later, as this vulnerability has been widely exploited in the wild. Additionally, implementing network segmentation and access controls can help limit the potential impact of such attacks by restricting access to the libvirt daemon to trusted networks and users only. The fix implemented in version 1.1.3 addresses the core issue by ensuring that proper identity context is maintained during connection termination, preventing the use-after-free condition that was enabling the denial of service attack.